1. Field of the Invention
The present invention relates to a light pipe and a planar polarized-light source which can convert incident light received from its side face to linearly polarized light having uniform brightness which is then emitted from both surfaces thereof under control over oscillating surfaces so that they are suitable for the formation of back light for liquid crystal display device.
The present application is based on Japanese Patent Applications No. Hei. 11-131429, 11-131430, 11-138102, 11166727, 11-174368 and 11-197083, which are incorporated herein by reference.
2. Description of the Related Art
As a side light type light-pipe which can be used as back light for liquid crystal device there has heretofore been known a device comprising a light-emitting means made of reflecting dots or the like provided on a light-transmitting resin plate having an arrangement such that transmitted light produced by total reflection is emitted from one of two surfaces of the plate by scattering or the like. However, the foregoing emitted light is natural light which has little or no polarization and thus needs to be converted to linearly polarized light through a polarizing plate before liquid crystal display. Therefore, the foregoing device is disadvantageous in that the polarizing plate causes absorption loss that prevents the percent utilization of light from exceeding 50%.
Under the foregoing circumstances, a system comprising in addition to the foregoing arrangement a polarized-light converting means having a polarized-light separating plate which utilizes Brewster angle to give linearly polarized light and a retarder plate in combination has been proposed (JP-A-6-18873 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-6-160840, JP-A-6-265892, JP-A-7-72475, JP-A-7-261122, JP-A-7-270792, JP-A-9-54556, JP-A-9-105933, JP-A-9-138406, JP-A-9-152604, JP-A-9-293406, JP-A-9-326205, JP-A-10-78581). However, such a back light cannot provide sufficient polarization and can hardly give control over the polarization direction. Thus, such a back light can hardly be put in practical use.